1. Field of the Invention
The present invention mainly relates to a magnetic sensing element used for a hard disk and magnetic sensor, in particular to a magnetic sensing element being excellent in reproductive properties even in a narrow track-width structure, and a method for manufacturing the same.
2. Description of the Related Art
FIG. 35 is a partial cross section of the structure of a conventional magnetic sensing element viewed from the opposed face side to a magnetic recording medium.
In FIG. 35, the reference numeral 1 denotes a substrate, and a multilayer 6 comprising a first antiferromagnetic layer 2, a pinned magnetic layer 3, a nonmagnetic layer 4 and a free magnetic layer 5 are formed on the substrate 1. A ferromagnetic layer 7 and a second antiferromagnetic layer 8 are formed on each side region of the free magnetic layer 5, and an electrode layer 9 is formed on each second antiferromagnetic layer 8.
Magnetization of the pinned magnetic layer 3 is fixed in the Y-direction in the drawing by an exchange coupling magnetic field generated between the pinned magnetic layer and first antiferromagnetic layer 2. Magnetization of the ferromagnetic layers 7 located under each second antiferromagnetic layer 8 and magnetization at each side region C of the free magnetic layer 5 are tightly fixed in the X-direction in the drawing by an exchange magnetic field generated between the second antiferromagnetic layer 8 and these layers, and the central region D of the free magnetic layer 5 in the track width region Tw is weakly put into a single magnetic domain state to an extent capable of magnetic variation against an external magnetic field.
The method for controlling magnetization of the free magnetic layer 5 using a pair of the second antiferromagnetic layers 8 and 8 as shown in FIG. 35 is called an exchange bias method, and the optical track width Tw is defined by the distance between the second antiferromagnetic layers 8 in the track width direction (X-direction) as shown in FIG. 35.
Since the direction of magnetization of the free magnetic layer 5 is tightly fixed at each side region C of the free magnetic layer 5 located below each second antiferromagnetic layer 8 in the magnetic sensing element employing the exchange bias method, magnetization can be readily varied at the entire region of the central region D. In other words, substantially no region where magnetization is not varied by the external magnetic field—or a so called dead zone—exists within the optical track width Tw of the magnetic sensing element shown in FIG. 34. Accordingly, this magnetic sensing element is excellent in complying with a narrow track width structure.
It is required in recent years to reduce the optical track width of the magnetic sensing element to 0.15 μm or less, particularly in the range of 0.10 to 0.12 μm. However, the output of the sensed magnetic field of the magnetic sensing element is extremely reduced at an optical track width of 0.15 μm or less even in the magnetic sensing element using the exchange bias method.
FIG. 36 is a graph showing the relation between the optical track width and output of the sensed magnetic field in the exchange bias magnetic sensing element shown in FIG. 35. The output of the sensed magnetic field is obtained as a voltage change from the magnetic sensing element. In this graph, the ratio of the height MRh of the element to the optical track width is defined to be 0.75.
The first antiferromagnetic layer 2 and the second antiferromagnetic layers 8 are made of a PtMn alloy, the pinned magnetic layer 3 is made of a CoFe alloy, the nonmagnetic layer 4 is made of Cu, the free magnetic layer 5 is made of a Ni80Fe20 alloy or Co, and the electrode layers 9 are made of Cr.
In the graph in FIG. 36, the curve indicated by the marks (⋄) shows the result using the free magnetic layer 5 made of the Ni80Fe20 alloy, and the curve indicated by the marks (□) shows the result using the free magnetic layer 5 made of Co.
FIG. 36 shows that the output of the sensed magnetic field becomes small as the optical track width is reduced. Particularly, the output of the sensed magnetic field rapidly decreases when the optical track width is decreased to 0.12 μm or less, particularly to 0.1 μm or less.
The same results were obtained when the free magnetic layer 5 is made of a Co90Fe10 alloy.